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Diffstat (limited to 'SRC/slagtm.f')
| -rw-r--r-- | SRC/slagtm.f | 190 |
1 files changed, 190 insertions, 0 deletions
diff --git a/SRC/slagtm.f b/SRC/slagtm.f new file mode 100644 index 00000000..cd58ceef --- /dev/null +++ b/SRC/slagtm.f @@ -0,0 +1,190 @@ + SUBROUTINE SLAGTM( TRANS, N, NRHS, ALPHA, DL, D, DU, X, LDX, BETA, + $ B, LDB ) +* +* -- LAPACK auxiliary routine (version 3.1) -- +* Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd.. +* November 2006 +* +* .. Scalar Arguments .. + CHARACTER TRANS + INTEGER LDB, LDX, N, NRHS + REAL ALPHA, BETA +* .. +* .. Array Arguments .. + REAL B( LDB, * ), D( * ), DL( * ), DU( * ), + $ X( LDX, * ) +* .. +* +* Purpose +* ======= +* +* SLAGTM performs a matrix-vector product of the form +* +* B := alpha * A * X + beta * B +* +* where A is a tridiagonal matrix of order N, B and X are N by NRHS +* matrices, and alpha and beta are real scalars, each of which may be +* 0., 1., or -1. +* +* Arguments +* ========= +* +* TRANS (input) CHARACTER*1 +* Specifies the operation applied to A. +* = 'N': No transpose, B := alpha * A * X + beta * B +* = 'T': Transpose, B := alpha * A'* X + beta * B +* = 'C': Conjugate transpose = Transpose +* +* N (input) INTEGER +* The order of the matrix A. N >= 0. +* +* NRHS (input) INTEGER +* The number of right hand sides, i.e., the number of columns +* of the matrices X and B. +* +* ALPHA (input) REAL +* The scalar alpha. ALPHA must be 0., 1., or -1.; otherwise, +* it is assumed to be 0. +* +* DL (input) REAL array, dimension (N-1) +* The (n-1) sub-diagonal elements of T. +* +* D (input) REAL array, dimension (N) +* The diagonal elements of T. +* +* DU (input) REAL array, dimension (N-1) +* The (n-1) super-diagonal elements of T. +* +* X (input) REAL array, dimension (LDX,NRHS) +* The N by NRHS matrix X. +* LDX (input) INTEGER +* The leading dimension of the array X. LDX >= max(N,1). +* +* BETA (input) REAL +* The scalar beta. BETA must be 0., 1., or -1.; otherwise, +* it is assumed to be 1. +* +* B (input/output) REAL array, dimension (LDB,NRHS) +* On entry, the N by NRHS matrix B. +* On exit, B is overwritten by the matrix expression +* B := alpha * A * X + beta * B. +* +* LDB (input) INTEGER +* The leading dimension of the array B. LDB >= max(N,1). +* +* ===================================================================== +* +* .. Parameters .. + REAL ONE, ZERO + PARAMETER ( ONE = 1.0E+0, ZERO = 0.0E+0 ) +* .. +* .. Local Scalars .. + INTEGER I, J +* .. +* .. External Functions .. + LOGICAL LSAME + EXTERNAL LSAME +* .. +* .. Executable Statements .. +* + IF( N.EQ.0 ) + $ RETURN +* +* Multiply B by BETA if BETA.NE.1. +* + IF( BETA.EQ.ZERO ) THEN + DO 20 J = 1, NRHS + DO 10 I = 1, N + B( I, J ) = ZERO + 10 CONTINUE + 20 CONTINUE + ELSE IF( BETA.EQ.-ONE ) THEN + DO 40 J = 1, NRHS + DO 30 I = 1, N + B( I, J ) = -B( I, J ) + 30 CONTINUE + 40 CONTINUE + END IF +* + IF( ALPHA.EQ.ONE ) THEN + IF( LSAME( TRANS, 'N' ) ) THEN +* +* Compute B := B + A*X +* + DO 60 J = 1, NRHS + IF( N.EQ.1 ) THEN + B( 1, J ) = B( 1, J ) + D( 1 )*X( 1, J ) + ELSE + B( 1, J ) = B( 1, J ) + D( 1 )*X( 1, J ) + + $ DU( 1 )*X( 2, J ) + B( N, J ) = B( N, J ) + DL( N-1 )*X( N-1, J ) + + $ D( N )*X( N, J ) + DO 50 I = 2, N - 1 + B( I, J ) = B( I, J ) + DL( I-1 )*X( I-1, J ) + + $ D( I )*X( I, J ) + DU( I )*X( I+1, J ) + 50 CONTINUE + END IF + 60 CONTINUE + ELSE +* +* Compute B := B + A'*X +* + DO 80 J = 1, NRHS + IF( N.EQ.1 ) THEN + B( 1, J ) = B( 1, J ) + D( 1 )*X( 1, J ) + ELSE + B( 1, J ) = B( 1, J ) + D( 1 )*X( 1, J ) + + $ DL( 1 )*X( 2, J ) + B( N, J ) = B( N, J ) + DU( N-1 )*X( N-1, J ) + + $ D( N )*X( N, J ) + DO 70 I = 2, N - 1 + B( I, J ) = B( I, J ) + DU( I-1 )*X( I-1, J ) + + $ D( I )*X( I, J ) + DL( I )*X( I+1, J ) + 70 CONTINUE + END IF + 80 CONTINUE + END IF + ELSE IF( ALPHA.EQ.-ONE ) THEN + IF( LSAME( TRANS, 'N' ) ) THEN +* +* Compute B := B - A*X +* + DO 100 J = 1, NRHS + IF( N.EQ.1 ) THEN + B( 1, J ) = B( 1, J ) - D( 1 )*X( 1, J ) + ELSE + B( 1, J ) = B( 1, J ) - D( 1 )*X( 1, J ) - + $ DU( 1 )*X( 2, J ) + B( N, J ) = B( N, J ) - DL( N-1 )*X( N-1, J ) - + $ D( N )*X( N, J ) + DO 90 I = 2, N - 1 + B( I, J ) = B( I, J ) - DL( I-1 )*X( I-1, J ) - + $ D( I )*X( I, J ) - DU( I )*X( I+1, J ) + 90 CONTINUE + END IF + 100 CONTINUE + ELSE +* +* Compute B := B - A'*X +* + DO 120 J = 1, NRHS + IF( N.EQ.1 ) THEN + B( 1, J ) = B( 1, J ) - D( 1 )*X( 1, J ) + ELSE + B( 1, J ) = B( 1, J ) - D( 1 )*X( 1, J ) - + $ DL( 1 )*X( 2, J ) + B( N, J ) = B( N, J ) - DU( N-1 )*X( N-1, J ) - + $ D( N )*X( N, J ) + DO 110 I = 2, N - 1 + B( I, J ) = B( I, J ) - DU( I-1 )*X( I-1, J ) - + $ D( I )*X( I, J ) - DL( I )*X( I+1, J ) + 110 CONTINUE + END IF + 120 CONTINUE + END IF + END IF + RETURN +* +* End of SLAGTM +* + END |